1. Field of the Invention
Aspects of the invention relate to a pixel and an organic light emitting display using the same, and more particularly to a pixel capable of compensating for the threshold voltage of a transistor of the pixel and for deterioration of the pixel, and an organic light emitting display using the same.
2. Description of the Related Art
Due to recent advances in thin film transistor (TFT) technology, active matrix type flat panel displays that display images using TFTs have become widely used. In particular, organic light emitting displays having high emission efficiency, brightness, and response speed and a large viewing angle have been in the spotlight recently.
An organic light emitting display displays an image using a plurality of organic light emitting diodes (OLEDs). An OLED includes an anode electrode, a cathode electrode, and an organic light emitting layer disposed between the anode electrode and the cathode electrode to emit light resulting from recombination of electrons and holes.
FIG. 1 is a circuit diagram of a pixel used in an organic light emitting display according to the related art. Referring to FIG. 1, the pixel includes a first transistor T1, a second transistor T2, a capacitor Cst, and an organic light emitting diode (OLED).
The source of the first transistor T1 is coupled to a first power source ELVDD, the drain of the first transistor T1 is coupled to the OLED, and the gate of the first transistor T1 is coupled to a node N. The source of the second transistor T2 is coupled to a data line Dm, the drain of the second transistor T2 is coupled to the node N, and the gate of the second transistor T2 is coupled to a scan line Sn. The first electrode of the capacitor Cst is coupled to the first power source ELVDD, and the second electrode of the capacitor Cst is coupled to the node N. The OLED includes an anode electrode, a cathode electrode, and a light emitting layer disposed between the anode electrode and the cathode electrode. The anode electrode is coupled to the drain of the first transistor T1, and the cathode electrode is coupled to a second power source ELVSS. When current flows from the anode electrode to the cathode electrode in the OLED, the light emitting layer emits light having a brightness that depends on the magnitude of the current flowing in the OLED. The following Equation 1 expresses the current that flows in the OLED.
                              I          d                =                              β            2                    ⁢                                    (                              ELVDD                -                Vdata                -                Vth                            )                        2                                              (        1        )            where Id is the current that flows in the OLED, Vdata is the voltage of a data signal applied to the data line Dm, ELVDD is the voltage of the first power source applied to the source of the first transistor T1, Vth is the threshold voltage of the first transistor T1, and β is a constant.
Referring to Equation 1, the current that flows in the OLED depends on the voltage ELVDD of the first power source, the voltage Vdata of the data signal, and the threshold voltage Vth of the first transistor T1. Therefore, the current that flows in the OLED varies in accordance to the voltage deviation of the first power source ELVDD applied to each pixel and the deviation of the threshold voltage of the first transistor T1, thereby causing a deviation in the brightness of the OLED. In addition, when current flows in the OLED for a long time, the OLED deteriorates so that the brightness of the light that is generated varies even though the same current flows, thereby deteriorating picture quality.